Manufacturing method for bearing member, bearing member, motor and disk drive

ABSTRACT

A sleeve has a thrust dynamic pressure generating groove arrangement for generating a dynamic pressure in a thrust direction between another member and the sleeve. The sleeve is formed in the following manner. First, a mold is prepared which is provided with a portion corresponding to the thrust dynamic pressure generating groove arrangement. Injection molding is carried out by using this mold and material containing binders and metal particulates, thereby forming a work-in-process piece having the thrust dynamic pressure groove arrangement in a cavity of the mold. Then, binders in the work-in-process piece are removed by heating, and thereafter metal particulates in the work-in-process piece are sintered.

FIELD OF THE INVENTION

The present invention relates to a bearing member for use in a bearing, a manufacturing method for the bearing member, an electric motor, and a disk drive including a motor.

DESCRIPTION OF THE RELATED ART

Disk drives such as hard disk drives include spindle motors (hereinafter, referred to as “motors”) which rotate disk-shaped recording media (hereinafter, simply referred to as “disks”). One exemplary motor put into practical use includes a fluid dynamic pressure bearing. The fluid dynamic pressure bearing supports a rotor portion of the motor in a rotatable manner relative to a stationary portion of the motor by utilizing a dynamic pressure of lubricant oil. In the fluid dynamic pressure bearing, a shaft connected to the rotor portion is supported in a non-contact manner by the lubricant oil. Thus, the rotor portion can be rotated precisely and with low noise.

When the aforementioned motor has a thrust dynamic pressure portion which generates a dynamic pressure in a thrust direction, a bearing member of the motor, e.g., a sleeve, is provided with a plurality of grooves for generating the thrust dynamic pressure (hereinafter, referred to as “thrust dynamic pressure generating grooves”), and a communication hole or groove for adjusting the pressure in the fluid dynamic pressure bearing.

For example, a sleeve having thrust dynamic pressure generating grooves, which is made of solid material, is described. An example of the solid material is stainless steel. That sleeve is usually manufactured in the following manner. First, a hollow, cylindrical member is formed by cutting. The thrust dynamic pressure generating grooves are formed on the hollow, cylindrical member by an electrolytic process. That is, formation of the dynamic pressure generating grooves is carried out as a separate step from the cutting step for forming the hollow, cylindrical member. Alternatively, the thrust dynamic pressure generating grooves may be formed by cutting using a fine cutter. In this case, however, it takes a relatively long time to form a number of grooves, the lifetime of the cutter is shortened, and the manufacturing cost of the sleeve is increased.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a manufacturing method for a bearing member having a thrust dynamic pressure groove arrangement is provided. In the manufacturing method, first, a mold is prepared which is provided with a portion corresponding to the thrust dynamic pressure generating groove arrangement of the bearing member. Then, a work-in-process piece for the bearing member, which has the thrust dynamic pressure generating groove arrangement, is formed in a cavity of the mold by injection molding. A material for the bearing member contains binders and metal particulates having an average particle diameter of 10 μm or less. Then, the binders in the work-in-process piece are removed by heating, and thereafter the metal particulates in the work-in-process piece are sintered. The depth of each groove in the thrust dynamic pressure generating groove arrangement is 20 μm or less. The bearing member is manufactured through the above steps.

According to another preferred embodiment of the present invention, a bearing member having a thrust dynamic pressure generating groove arrangement or a communication hole or groove can be manufactured efficiently.

It is possible to efficiently manufacture a sleeve or sleeve housing which has thrust dynamic pressure generating grooves.

Further, it is possible to efficiently infuse into a mold, a material for the bearing member.

Only selected embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an internal structure of a disk drive according to a first preferred embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of a motor according to the first preferred embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view of a sleeve according to the first preferred embodiment of the present invention.

FIG. 4 is a bottom view of the sleeve of FIG. 3.

FIG. 5 is an enlarged vertical cross-sectional view of the motor of FIG. 2.

FIG. 6 shows steps in a procedure for manufacturing the sleeve according to the first preferred embodiment of the present invention.

FIG. 7 is a cross-sectional view of a mold used in the first preferred embodiment of the present invention.

FIG. 8 is a cross-sectional view of a work-in-process piece for the sleeve according to the first preferred embodiment of the present invention.

FIGS. 9A, 9B, and 9C show other exemplary molds in the first preferred embodiment of the present invention.

FIG. 10 shows another exemplary sleeve in the first preferred embodiment of the present invention.

FIG. 11 shows an upper end surface of the sleeve of FIG. 10.

FIG. 12 is a vertical cross-sectional view of a motor according to a second preferred embodiment of the present invention.

FIG. 13 is a vertical cross-sectional view of a sleeve according to the second preferred embodiment of the present invention.

FIG. 14 shows an upper end surface of the sleeve of FIG. 13.

FIG. 15 is a cross-sectional view of a mold used in the second preferred embodiment of the present invention.

FIGS. 16A, 16B, and 16C show other exemplary molds in the second preferred embodiment of the present invention.

FIG. 17 is a vertical cross-sectional view of a motor according to a third preferred embodiment of the present invention.

FIG. 18 is a vertical cross-sectional view of a sleeve housing according to the third preferred embodiment of the present invention.

FIG. 19 is a cross-sectional view of a mold used in the third preferred embodiment of the present invention.

FIG. 20 shows another exemplary mold in the third preferred embodiment of the present invention.

FIG. 21 shows another shape of thrust dynamic pressure generating grooves in the third preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are now described, referring to FIGS. 1 through 21.

In the explanation of the invention, when a positional relationship of respective parts and a direction are explained using words such as up, down, right and left, such positional relation and direction are based on the drawings, but they are not a positional relation or a direction as actually assembled in an apparatus.

Embodiment 1

FIG. 1 shows an internal structure of a disk drive 60 having an electric spindle motor 1 (hereinafter, referred to as “motor 1”) according to a first preferred embodiment of the present invention. The disk drive 60 is a hard disk drive and includes a disk-shaped storage medium 62 (hereinafter, referred to as “disk 62”) for storing information, an access portion 63, the electric motor 1 which retains and rotates the disk 62, and a housing 61.

The access portion 63 carries out at least one of writing and reading of information for the disk 62. The housing 61 accommodates the disk 62, the access portion 63 and the motor 1 in its internal space 110.

As shown in FIG. 1, the housing 61 includes an approximately cup-shaped first housing member 611 open upward and a second housing member 612 in the form of a plate. The motor 1 and the access portion 63 are attached onto a bottom of the housing 61 inside the housing 61. The second housing member 612 covers the opening of the first housing member 611, thereby defining the internal space 110.

The housing 61 is formed by joining the second housing member 612 to the first housing member 611. The internal space 110 is a clean space having an extremely small amount of dust.

The disk 62 is placed on an upper side of the motor 1, and is secured to the motor 1 with a damper 621.

The access portion 63 includes a head 631, an arm 632 for supporting the head 631, and a head moving portion 633. The head 631 accesses the disk 62 and can perform at least one of writing and reading of information for the disk 62 in a magnetic manner. The head moving portion 633 moves the arm 632 to change a relative position of the head 631 with respect to the disk 62. With this configuration, the head 631 accesses a desired position of the disk 62 to perform at least one of writing and reading of information, while being close to the rotating disk 62.

FIG. 2 is a vertical cross-sectional view of the motor 1. FIG. 2 shows a cross section of the motor 1, taken along a plane including a center axis J1 of the motor 1 (which also serves a center axis of a sleeve unit 5 that will be described later). A structure existing behind the cross section is partially shown with broken line.

Referring to FIG. 2, the motor 1 includes a stationary portion 2 and a rotor portion 3. The rotor portion 3 is supported by a bearing in a rotatable manner around the center axis J1 relative to the stationary portion 2. The bearing utilizes a dynamic pressure of lubricant oil. In the following description, for the sake of convenience, a side closer to the rotor portion 3 is called as an upper side, and a side closer to the stationary portion 2 is called as a lower side. However, it is not always necessary that the center axis J1 is coincide with a direction of gravity.

The rotor portion 3 includes a rotor hub 31 which retains various portions of the rotor portion 3, and a rotor magnet 34 which is mounted on the rotor hub 31 and arranged around the center axis J1.

The rotor hub 31 is integrally formed from stainless or the like, and includes a shaft 311, a plate portion 312 in the form of an approximately circular plate, and a hollow, approximately cylindrical portion 313. The shaft 311 is hollow and approximately cylindrical and centered on the center axis J1, and projects axially downward. The plate portion 312 spreads perpendicularly to the center axis J1 from an axially upper end of the shaft 311. The cylindrical portion 313 projects downward from an outer edge of the plate portion 312. A thrust plate 314 in the form of an approximately circular plate is attached to an axially lower end of the shaft 311.

The stationary portion 2 includes: a base plate 21 serving as a base portion which holds various portions of the stationary portion 2; a hollow, approximately cylindrical sleeve unit 5; and a stator 24. The sleeve unit 5 receives the shaft 311 of the rotor portion 3 therein and forms a part of the bearing which supports the rotor portion 3 in a rotatable manner. The stator 24 is attached to the base plate 21 around the sleeve unit 5.

The base plate 21 is a part of the first housing member 611 (see FIG. 1), and is formed by pressing a member in the form of a plate made of aluminum, aluminum alloy, or magnetic or non-magnetic iron-based metal. The base plate 21 is integrally formed with other portions of the first housing member 611.

The stator 24 generates a torque around the center axis J1 between the stator 24 and the rotor magnet 34 arranged around the shaft 311. That is, the stator 24 and the rotor magnet 34 form together a driving mechanism of the motor 1, which rotates the rotor portion 3 around the center axis J1 relative to the stationary portion 2.

The stator 24 is attached to the base plate 21 from above by interference fitting and/or bonding. The stator 24 includes a core 241 formed by a plurality of silicon steel plates which are stacked, and a plurality of coils 242 provided at a predetermined portion of the core 241.

The core 241 includes teeth 243 and an annular core back 244. The teeth 243 are radially arranged around the center axis J1. The core back 244 supports the teeth 243 from an outer peripheral side of the teeth 243. That is, the core back 244 connects and supports distal-ends of the teeth 243. Please note that the distal-end of the tooth 243 is a farther one of ends of that tooth 243 from the central axis J1.

Portions of the silicon steel plates forming the core 241, which correspond to the teeth 243 and the core back 244, respectively, are integrally formed with each other. Thus, the teeth 243 and the core back 244 are magnetically connected to each other.

The coil 242 is formed by winding a conductive wire around the tooth 243 in a multilayered (e.g., two-layered) way. A conductive wire from each coil 242 is caught on a hook 247 formed between the adjacent teeth 243, is directed to a circuit board 248, and is soldered to an electrode of the circuit substrate 248.

The base plate 21 is provided at its center with a hollow, approximately cylindrical base cylindrical portion 216 which projects axially upward, i.e., toward the rotor portion 3. The base cylindrical portion 216 is arranged coaxially with the center axis J1. As shown in FIG. 2, the sleeve unit 5 includes a sleeve 51, and a hollow, approximately cylindrical sleeve housing 52. The sleeve 51 is hollow and approximately cylindrical and centered on the center axis J1. The shaft 311 is inserted into the sleeve 51. The sleeve housing 52 is attached to an outer circumference of the sleeve 51, and is inserted into the base cylindrical portion 216 and secured to the base plate 21.

A flange portion 521 is formed in an axially upper part of the sleeve housing 52 integrally therewith. The flange portion 521 projects radially outward and is arranged along the outer circumference of the sleeve unit 5. When the sleeve unit 5 is installed, the outer periphery of the flange portion 521 engages with the base cylindrical portion 216 in the axial direction. A lower end opening of the sleeve unit 5 is closed with a seal cap 59 in the form of an approximately circular plate.

FIG. 3 is an enlarged vertical cross-sectional view of the sleeve 51. FIG. 4 is a bottom view of the sleeve 51.

The sleeve 51 has a lower end surface 511 which is perpendicular to the center axis J1. As shown in FIG. 4, a plurality of spiral grooves are formed in the lower end surface 511. In the following description, a group of the plurality of grooves shown in FIG. 4 is called as a thrust dynamic pressure generating groove arrangement 513.

The depth of each groove is 20 μm or less in the axial direction, and preferably 5 μm or more and 15 μm or less. A communication groove 512 extending along the axial direction is formed in a portion of an outer circumferential surface of the sleeve 51. As will be described later, the thrust dynamic pressure generating groove arrangement 513 generates a dynamic pressure in the thrust direction in the bearing when the motor 1 is driven, and the communication groove 512 adjusts a pressure of lubricant oil in the bearing.

A hollow cylindrical portion 531 of the sleeve 51 shown in FIG. 3 is provided with a thrust dynamic pressure portion 532 having the thrust dynamic pressure generating groove arrangement 513 formed therein, and a pressure adjusting portion 533 having the communication groove 512 which adjusts the pressure of the lubricant oil.

Radially outer and inner rims of an axially upper end of the sleeve 51 shown in FIG. 3 and radially outer and inner rims of the axially lower end of the sleeve 51 shown in FIG. 4 are chamfered to be inclined with respect to the axially upper and lower end surfaces. When seen in the axial direction, the inner and outer chamfered portions are arranged annularly around the center axis J1 at the radially outer and inner rims of each of the upper and lower end surfaces of the sleeve 51 (except for a portion of the communication groove 512).

In this preferred embodiment, the sleeve 51 is formed by metal injection molding, as described later. Thus, a porous ratio of the sleeve 51 is close to that of solid material. For example, the porous ratio of the sleeve 51 is 95% or higher when a porous ratio of fine stainless steel is defined as 100%. In addition, an outer surface of the sleeve 51 is smoother than that of a member which is formed only by a normal mechanical machining process.

Next, the bearing utilizing a dynamic pressure of lubricating oil for supporting the rotor portion 3 of the motor 1 in a rotatable manner relative to the stationary portion 2 is described. FIG. 5 is an enlarged vertical cross-sectional view of a portion of the motor 1 (left half in FIG. 2).

As shown in FIG. 5, small gaps are formed between a lower surface of the plate portion 312 of the rotor hub 31 and an upper end surface of the sleeve housing 52, between an inner circumferential surface of the sleeve 51 and an outer circumferential surface of the shaft 311, between a lower end surface of the sleeve 51 and an upper surface of the thrust plate 314, between a lower surface of the thrust plate 314 and an upper surface of the seal cap 59, and between an outer peripheral surface of the flange portion 521 of the sleeve housing 52 and an inner circumferential surface of the cylindrical portion 313 of the rotor hub 31. These gaps are called as “upper gap 41”, “side gap 42”, “first lower gap 43”, “second lower gap 44”, and “outer gap 45”, respectively. These gaps are continuously filled with lubricant oil and are formed by the rotor hub 31, the thrust plate 314, the sleeve 51, the sleeve housing 52, and the seal cap 59.

The outer peripheral surface of the flange portion 521 of the sleeve housing 52 is inclined with respect to the center axis J1 in such a manner that an outer diameter of the flange portion 521 gradually decreases downward in the axial direction. The inner circumferential surface of the cylindrical portion 313 of the rotor hub 31, which faces the outer peripheral surface of the flange portion 521, is parallel to the center axis J1. That is, an inner diameter the cylindrical portion 313 is constant. Thus, an interface of lubricant oil in the outer gap 45 is meniscus in shape due to capillary action and surface tension. Hence, the outer gap 45 serves as an oil buffer and a tapered seal for preventing lubricant oil from flowing out.

The thrust dynamic pressure generating groove arrangement 513 is formed in the lower end surface 511 of the sleeve 51, as described above. The thrust dynamic pressure generating groove arrangement 513 generates a pressure in lubricant oil toward the center axis J1 when the rotor portion 3 rotates. The upper end surface 522 of the sleeve housing 52 is also provided with a similar thrust dynamic pressure generating groove arrangement. Thus, a thrust dynamic pressure bearing portion is formed at each of the first lower gap 43 and the upper gap 41. The thrust dynamic pressure generating groove arrangement formed in the upper end surface 522 of the sleeve housing 52 generates a dynamic pressure in the thrust direction between the lower surface of the plate portion 312 and the upper end surface 522 of the sleeve housing 52. The dynamic pressure generated in the first lower gap 43 and that generated in the upper gap 41 are adjusted to be approximately equal to each other by the communication groove 512 during an operation of the motor 1.

In the side gap 42, the outer circumferential surface of the shaft 311 is provided with a plurality of grooves for generating a dynamic pressure in lubricant oil. That is, a radial dynamic pressure bearing portion is formed at the side gap 42. The grooves are herringbone grooves provided in axially upper and axially lower portions of the outer circumferential surface of the shaft 311. A group of those grooves is hereinafter called as a radial dynamic pressure generating groove arrangement.

In the motor 1, the rotor portion 3 is supported by the bearing utilizing a dynamic pressure via lubricant oil in a non-contact manner. With this configuration, the rotor portion 3 can be rotated precisely and with low noise. Especially in this preferred embodiment, abnormal contact between the shaft 311 and the sleeve 51 caused by air bubbles generated in lubricant oil, and leakage of lubricant oil caused by expansion of air in the bearing can be further suppressed.

In the motor 1, the gaps formed between the sleeve unit 5, the rotor hub 31, and the seal cap 59 (i.e., the upper gap 41, the side gap 42, the first lower gap 43, the second lower gap 44 and the outer gap 45) are filled with lubricant oil which is an example of fluid. During rotation of the rotor portion 3, the rotor portion 3 is supported by the dynamic pressure of the lubricant oil. The rotor portion 3 is rotated around the center axis J1 relative to the stationary portion 2, thereby rotating the disk 62 mounted on the rotor portion 3 (see FIG. 1).

Next, a method for forming the sleeve 51 in this preferred embodiment is described, referring to FIG. 6. In this preferred embodiment, the sleeve 51 is formed by metal injection molding. When the sleeve 51 shown in FIG. 3 is formed, a mold is prepared which is provided therein with portions respectively corresponding to the thrust dynamic pressure generating groove arrangement 513 and the communication groove 512 of the sleeve 51 (step S11).

FIG. 7 is a schematic cross-sectional view of a mold 91 used for forming the sleeve 51. In FIG. 7, the mold 91 is illustrated as one integral mold, but in the actual case, the mold 91 includes a plurality of mold parts which are combined with each other and can be separated from each other. The mold 91 may include any combination of mold parts (this description is also applied to other preferred embodiments described later).

As shown in FIG. 7, the mold 91 is provided therein with a portion 911 shaped to form the thrust dynamic pressure generating groove arrangement 513 of the sleeve 51, and a portion 912 shaped to form the communication groove 512 of the sleeve 51. In the following description, the portion 911 is called as “dynamic pressure generating groove forming portion 911”, and the portion 912 is called as “communication groove forming portion 912”. The dynamic pressure generating groove forming portion 911 is provided at an axial end of a cavity of the mold 91.

A filling opening 913 through which material is infused into the mold 91 is provided on a side of the mold 91 opposite to the dynamic pressure generating groove forming portion 911. The filling opening 913 is arranged on the center axis J1 of the sleeve 51 to be formed (more precisely, a work-in-process piece 81 to be processed into the sleeve 51 as described later). The center axis J1 is also shown in FIGS. 9A to 9C, 15, 16A to 16C, 19 and 20.

The mold 91 is placed on a predetermined injection molding machine, and material for the sleeve 51 is injected and charged into the mold 91 through a nozzle of the injection molding machine.

Examples of the material for the sleeve 51 are stainless steel such as SUS304L, SUS316L, SUS410L, SUS430, SUS440C and SUS630, heat resistant steel such as SCH21, alloys of iron and nickel, Kovar, Invar, Super Invar, Permendur, Stellite (registered trademark), titanium, and copper. The material for the sleeve 51 contains particulates having an average particle diameter of 10 μm or less (preferably 6 μm or more) and binders. The particulates and the binders are mixed with each other and are then granulated. That is, the average particle diameter of metal particulates contained in the material for the sleeve 51 is 10 μm or less.

The material in the mold 91 is cooled through the mold 91, so as to be solidified. In this manner, a member having the thrust dynamic pressure generating groove arrangement 513 and the communication groove 512 (hereinafter referred to as “work-in-process piece”) is formed in the cavity of the mold 91 by injection molding using the material containing the metal particulates and the binders (step S12).

The work-in-process piece is taken out from the mold 91 by cutting at a position near the filling opening 913 and separating the mold 91 into mold parts. Then, as shown in FIG. 8, the work-in-process piece 81 is cut along chain double-dashed line A1, so that an unnecessary portion of the work-in-process piece 81 is removed.

The work-in-process piece 81 is heated for a long time to remove the binders contained therein (step S13). That is, a degreasing process is carried out. Then, the work-in-process piece 81 is heated at a higher temperature, thereby sintering the metal particulates contained in the work-in-process piece 81 (step S14). At this time, the work-in-process piece 81 is shrunk substantially uniformly, so that a sleeve 51 having the thrust dynamic pressure generating groove arrangement 513 in which the depth of each groove is 20 μm or less is formed. The forming of the sleeve 51 is thus completed. Please note that substantially uniform shrinkage of the work-in-process piece 81 means shrinkage of the work-in-process piece 81 with the variation in the amount of shrinkage within ±0.5%. In this manner, the sleeve 51 is formed by metal injection molding which includes the injection molding process, the degreasing process, and the sintering process in this preferred embodiment.

The sleeve 51 shown in FIG. 3 includes the thrust dynamic pressure generating groove arrangement 513 and the communication groove 512 and is formed by metal injection molding together with them. Thus, it is possible to efficiently form the sleeve 51 having the fine thrust dynamic pressure grooves and the communication groove 512. Similarly, the sleeve housing 52 may be formed together with the thrust dynamic pressure generating groove arrangement in the end surface 522 by metal injection molding.

As a method of forming a porous sintered sleeve, a sintering method is widely used. This widely-used sintering method usually uses particulates having a particle diameter of several tens of microns. This is because metal particulates having a particle diameter of several microns easily adhere to an inner wall of the mold in the molding process, making it difficult to appropriately infuse the particulates into the mold.

Thus, when the sintering method is used for forming a sleeve having fine thrust dynamic pressure generating grooves each having a depth of 20 μm or less, particulates may not be infused densely in a portion of the mold for forming the dynamic pressure generating grooves. In some cases, edges of the thrust dynamic pressure generating grooves are roughly formed, or the adjacent grooves are linked. Such edge shape of the thrust dynamic pressure generating groove may cause variation in a dynamic pressure generating performance such as efficiency for generating a pressure in lubricant oil toward the center axis. The influence of the variation in the dynamic pressure generating performance on the rotation characteristics of the motor increases as the motor is reduced in size.

Moreover, in the sleeve formed by the widely-used sintering method, a density of a portion sandwiched between the thrust dynamic pressure generating grooves becomes low and the number of air bubbles is increased. Thus, the substantial depths of the grooves are varied between the grooves, varying the bearing performance. In the sintering method, particulates having a particle diameter of several microns may be subjected to pretreatment into cluster shapes in order to increase the particle diameter. In this case, the particulate clusters are infused into the mold. However, the manufacturing cost of the sleeve is increased, and in this case also, the density cannot be increased sufficiently.

On the other hand, in metal injection molding used in this preferred embodiment, a mixture of particulates and binders is injected into the mold under high pressure. Thus, particulates having a particle diameter of 10 μm or less can appropriately be infused into the mold, resulting in dense infusing of the particulates in the dynamic pressure generating groove forming portion of the mold. It is also possible to prevent deterioration of the edge shape of the resultant thrust dynamic pressure generating groove. Further, the density of the portion sandwiched between the thrust dynamic pressure generating grooves is increased (air bubble is extremely small), and the depths of the grooves become constant. In this manner, the thrust dynamic pressure generating groove arrangement is formed precisely. Accordingly, the dynamic pressure performance of the fluid dynamic pressure bearing becomes constant. In addition, even in a small motor, the bearing performance can be stabilized.

FIGS. 9A to 9C show other exemplary molds for forming the work-in-process piece 81 for the sleeve 51. In a mold 91 a shown in FIG. 9A, a plurality of filling openings 913 are provided on a side of the mold 91 a opposite to the dynamic pressure generating groove forming portion 911 so as to respectively face outer edges of an end surface of the sleeve 51 to be formed. That end surface of the sleeve 51 is opposite to the end surface in which the thrust dynamic pressure generating groove arrangement 513 is formed.

In a mold 91 b shown in FIG. 9B, the filling opening 913 is provided at an axial end of the mold 91 b on the same side as the dynamic pressure generating groove forming portion 911. The filling opening 913 is arranged on the center axis J1 of the sleeve 51 to be formed. In a mold 91 c shown in FIG. 9C, a plurality of filling openings 913 are provided at positions of the mold 91 c which respectively face outer edges of an end surface of the sleeve 51 to be formed. In the same end surface of the sleeve 51 is formed the thrust dynamic pressure generating groove arrangement 513. As described above, molds having various structures may be used for injection molding for forming the sleeve 51.

It is preferable to infuse material into the mold via the filling opening(s) 913 located on the side of the mold opposite to the dynamic pressure generating groove forming portion 911, as in the mold 91 in FIG. 7 and the mold 91 a in FIG. 9A. This is because that the material can reliably be infused into the entire dynamic pressure generating groove forming portion 911 of the mold and the thrust dynamic pressure generating groove arrangement 513 of the sleeve 51 can be formed precisely.

For efficiently infusing the material into the mold, it is preferable that the filling opening 913 be arranged to face a portion of the hollow cylindrical portion 531 of the sleeve 51 to be formed. That portion is located at an axial end of the hollow cylindrical portion 531 on or near the center axis J1. In The mold 91 in FIG. 7 and the mold 91 b in FIG. 9 b, the filling opening 913 is arranged in that way.

In FIGS. 9A to 9C, the position of the mold at which the work-in-process piece 81 is cut is shown with chain double-dashed line A1. In FIGS. 15, 16A to 16C, 19 and 20 also, the position of the mold at which the work-in-process piece 81 is cut is shown with chain double-dashed line. According to a sleeve formed by the mold shown in FIGS. 9A to 9C, the cut plane is located at either one of an inner edge and an outer edge of an end surface which is perpendicular to the center axis J1. However, the cut plane may be located at a position other than the edge of the sleeve or work-in-process piece, depending upon the design of the mold. This can also be applied to second and third preferred embodiments which will be described later.

In this preferred embodiment, the thrust dynamic pressure generating groove arrangement 513 is formed in the lower end surface 511 of the sleeve 51 only. However, the thrust dynamic pressure generating grooves may be formed in the upper end surface of the sleeve 51 depending upon the design of the motor 1, instead of the upper end surface 522 of the sleeve housing 52.

FIG. 10 is a vertical cross-sectional view of another exemplary sleeve 51. FIG. 11 shows an upper end surface 514 of the sleeve 51 shown in FIG. 10. In the sleeve 51 shown in FIG. 11, an arrangement of thrust dynamic pressure generating grooves 515 formed in the upper end surface 514 is formed into spiral shapes oriented to the opposite side from the thrust dynamic pressure generating groove arrangement 513 (see FIG. 4) formed in the lower end surface 511 of the sleeve 51. In this case, when the rotor portion 3 rotates, a pressure of lubricating oil acting toward the center axis J1 is generated in the gap (see FIG. 5) between the upper end surface 514 of the sleeve 51 and the plate portion 312 of the rotor hub 31. Thus, a thrust dynamic pressure bearing portion is formed at this gap.

In the sleeve 51 shown in FIGS. 10 and 11, the thrust dynamic pressure generating groove arrangements 515 and 513 are formed in both the upper and lower end surfaces 514 and 511 simultaneously with the hollow cylindrical portion 531 by metal injection molding, respectively. Thus, it is possible to improve the manufacturing efficiency of the sleeve 51 provided at its both axial end surfaces with the thrust dynamic pressure generating groove arrangements 513 and 515.

In general, a porous sintered sleeve is formed by pressurizing and forming material such as metal powders and by sintering the same. Thus, a manufacturing error of length in a longitudinal direction (i.e., an axial direction parallel to the center axis) is serious as compared with a sleeve made of solid material. Especially in a structure in which the thrust dynamic pressure generating groove arrangement is formed in each of axial end surfaces of the sleeve, a large manufacturing error may make a gap size of a thrust gap different between motors. Thus, every motor has a different floating amount which affects the bearing performance. For this reason, it is preferable that the manufacturing error be small.

On the other hand, metal injection molding carried out in this preferred embodiment can make the manufacturing error relatively small. In this preferred embodiment, a sleeve having the thrust dynamic pressure generating groove arrangement at each of its axial end surfaces with is formed by metal injection molding. Thus, the sleeve in the preferred embodiment can be formed with high accuracy and with improved productivity.

Embodiment 2

A motor according to a second preferred embodiment of the present invention is now described. FIG. 12 is a vertical cross-sectional view of a motor 1 a of the second preferred embodiment, and shows only a left side of the center axis J1. In a motor 1 b shown in FIG. 17 also, only a left side of the center axis J1 is shown.

As shown in FIG. 12, the motor 1 a is an outer rotor type motor in which the rotor magnet 34 is arranged on a side of the stator 24 opposite to the center axis J1. A bearing structure in the motor 1 a is different from that of the motor 1 shown in FIG. 2. Except for the above, the motor 1 a is the same as the motor 1 in FIG. 2, and like parts are labeled with like reference numerals.

The bearing of the motor 1 a in FIG. 12 includes a sleeve 51 a having a shape similar to a shape obtained by integrally forming the sleeve 51 and the sleeve housing 52 in the motor 1 in FIG. 2. More specifically, the sleeve 51 a, which is hollow approximately cylindrical, is inserted into and fixed to the base cylindrical portion 216 provided on the base plate 21. The sleeve 51 a is provided at its upper portion with a flange portion 521 a.

The plate portion 312 of the rotor hub 31 is provided with a projection 315 which is hollow and cylindrical and has an inner surface facing the flange portion 521 a. A tapered seal is formed between the inner surface of the hollow cylindrical projection 315 and the flange portion 521 a. A surface of the sleeve 51 a is formed to be smooth by metal injection molding. Thus, the tapered seal of the motor 1 a can hold lubricant oil more reliably.

FIG. 13 is a vertical cross-sectional view of the sleeve 51 a. FIG. 14 shows an upper end surface 514 a of the sleeve 51 a. The upper end surface 514 a has an arrangement of thrust dynamic pressure generating grooves 515 a formed in its radially outer region. A thrust dynamic pressure bearing portion is formed at a gap between the upper end surface 514 a of the sleeve 51 a and the plate portion 312 of the rotor hub 31 (see FIG. 12). In the thrust dynamic pressure generating groove arrangement 515 a, the depth of each groove in the axial direction is 20 μm or less, and preferably 5 μm or more and 15 μm or less.

On the upper end surface 514 a in FIG. 14, an opening end of a communication hole 516 is arranged radially inside the thrust dynamic pressure generating groove arrangement 515 a. The communication hole 516 extends trough the sleeve 51 a to reach the lower end surface 511 of the sleeve 51 a. In the motor lain FIG. 12, the communication hole 516 is used for circulating lubricant oil in the bearing. Thus, the pressure of the lubricant oil in a gap between the upper end surface 514 a of the sleeve 51 a and the plate portion 312 of the rotor hub 31, and the pressure of the lubricant oil in a gap between the lower surface of the thrust plate 314 and an upper surface of the seal cap 59 are adjusted to be approximately equal to each other.

In this manner, in the sleeve 51 a in FIG. 13, a hollow cylindrical portion 531 a is provided with a thrust dynamic pressure portion 532 a having the thrust dynamic pressure generating groove arrangement 515 a for generating a thrust dynamic pressure, and a pressure adjusting portion 533 a having the communication hole 516 for adjusting a pressure of lubricant oil.

FIG. 15 is a schematic cross-sectional view of a mold 92 used for forming the sleeve 51 a. As shown in FIG. 15, the mold 92 is provided therein with a dynamic pressure generating groove forming portion 921 and a communication hole forming portion 922. The dynamic pressure generating groove forming portion 921 has a shape capable of forming the thrust dynamic pressure generating groove arrangement 515 a of the sleeve 51 a. The communication hole forming portion 922 has a shape capable of forming the communication hole 516 of the sleeve 51 a. The communication hole forming portion 922 is an independent pin which can be attached to and detached from the mold 92.

A filling opening 923 through which material for the sleeve 51 a is infused into the mold 92 is formed on a side of the mold 92 opposite to the dynamic pressure generating groove forming portion 921. In the mold 92 in FIG. 15, the filling opening 923 is arranged at a position on the center axis J1 of the sleeve 51 a to be formed.

When the sleeve 51 a is formed, the mold 92 shown in FIG. 15 is prepared (step S11 in FIG. 6), and then the mold 92 is placed in the injection molding machine.

A work-in-process piece having the thrust dynamic pressure generating groove arrangement 515 a and the communication hole 516 is formed in the cavity of the mold 92 by injection molding (step S12). Material for the sleeve 51 a contains metal particulates having an average particle diameter of 10 μm or less, which are the only metal material contained therein.

After the pin serving as the communication hole forming portion 922 is pulled out, the mold 92 is separated into mold parts and the formed work-in-process piece is taken out from the mold 92. Then, the work-in-process piece is cut along chain double-dashed line A2 in FIG. 15. After binders contained in the work-in-process piece are removed by heating, the particulates contained in the work-in-process piece are sintered (steps S13 and S14). In this manner, the sleeve 51 a is formed.

As described above, the sleeve 51 a shown in FIG. 13 includes the thrust dynamic pressure generating groove arrangement 515 a and the communication hole 516. The hollow cylindrical portion 531 a of the sleeve 51 a is formed by metal injection molding together with the thrust dynamic pressure generating groove arrangement 515 a and the communication hole 516.

Thus, the sleeve 51 a having the thrust dynamic pressure generating groove arrangement 515 a and the communication hole 516 can be manufactured efficiently. The thrust dynamic pressure generating groove arrangement may be formed in the lower end surface (see FIG. 12) of the sleeve 51 a which faces the thrust plate 314, instead of the upper end surface 514 a, or together with the upper end surface 514 a.

FIGS. 16A to 16C show other exemplary molds for forming the work-in-process piece of the sleeve 51 a. In a mold 92 a in FIG. 16A, a plurality of filling openings 923 are arranged on a side of the mold 92 a opposite to the dynamic pressure generating groove forming portion 921 so as to face outer edges of an end surface of the sleeve 51 a to be formed. In to a mold 92 b in FIG. 16B, the filling opening 923 is arranged on the same side of the mold 92 b as the dynamic pressure generating groove forming portion 921 to be located on the center axis J1 of the sleeve 51 a to be formed. In a mold 92 c in FIG. 16C, the filling openings 923 are arranged on the same side of the mold 92 c as the dynamic pressure generating groove forming portion 921 so as to face the outer edges of the end surface of the sleeve 51 a to be formed. Molds having various structures may be used for injection molding for producing the sleeve 51 a.

It is preferable that the material for the sleeve 51 a be infused into the mold from the filling opening(s) 923 arranged on the opposite side of the mold to the dynamic pressure generating groove forming portion 921, as in the mold 92 in FIG. 15 and the mold 92 a in FIG. 16A. This is because it is possible to reliably infuse the material for the sleeve 51 a into the entire dynamic pressure generating groove forming portion 921 of the mold, and to precisely form the thrust dynamic pressure generating groove arrangement 515 a of the sleeve 51 a.

For efficiently infusing the material for the sleeve 51 a into the mold, it is preferable to arrange the filling opening 923 at a position of the mold which faces a portion at an axial end of the hollow cylindrical portion 531 a (see FIG. 13) of the sleeve 51 a on or near the center axis J1, as in the mold 92 in FIG. 15 and the mold 92 b in FIG. 16B.

Embodiment 3

A motor according to a third preferred embodiment of the present invention is now described. FIG. 17 is a vertical cross-sectional view of a motor 1 b of the third preferred embodiment. As shown in FIG. 17, the motor 1 b is a so-called outer rotor type motor like the motor 1 a in FIG. 12. A bearing structure of the motor 1 b is different from those of the motor 1 a in FIG. 12 and the motor 1 in FIG. 2. Except for that, the motor 1 b is the same as the motor 1 in FIG. 2, and like parts are labeled with like reference numerals.

In a bearing of the motor 1 b in FIG. 17, a sleeve housing 52 b has a shape similar to a shape obtained by integrally forming the sleeve housing 52 and the seal cap 59 in the motor 1 in FIG. 2.

More specifically, the sleeve housing 52 b which is hollow and approximately cylindrical and has a bottom is inserted into and fixed to the base cylindrical portion 216 of the base plate 21. A tapered seal is formed between a inner surface of an annular projection 315 a attached to the plate portion 312 of the rotor hub 31 and a flange portion 521 b of the sleeve housing 52 b. Since a surface of the sleeve housing 52 b is formed to be smooth by metal injection molding in this preferred embodiment, the tapered seal of the motor 1 b can more reliably hold lubricant oil.

FIG. 18 is a vertical cross-sectional view of the sleeve housing 52 b. An upper end surface 522 of the sleeve housing 52 b has an arrangement of thrust dynamic pressure generating grooves 523 formed therein. A thrust dynamic pressure bearing portion is formed at a gap between the upper end surface 522 of the sleeve housing 52 b and the plate portion 312 of the rotor hub 31 (see FIG. 17). In the thrust dynamic pressure generating groove arrangement 523, the depth of each groove in the axial direction is 20 μm or less, and preferably 5 μm or more and 15 μm or less.

A communication groove 524 extending along the center axis J1 is formed in an inner circumferential surface of the sleeve housing 52 b. Another communication groove 517 extending in a direction perpendicular to the center axis J1 is formed in an axially lower end surface of a sleeve 51 b shown in FIG. 17. In the motor 1 b, the communication grooves 524 and 517 are used for circulating lubricant oil in the bearing. A pressure of lubricant oil in a gap between the axially upper end surface 522 of the sleeve housing 52 b and the plate portion 312 of the rotor hub 31, and a pressure of lubricant oil in a gap between an axially lower surface of the shaft 311 and the bottom of the sleeve housing 52 b are adjusted to be approximately equal to each other.

The sleeve housing 52 b in FIG. 18 includes a thrust dynamic pressure portion 542 having the thrust dynamic pressure generating groove arrangement 523, a pressure adjusting section 543 having the communication groove 524, and a hollow cylindrical portion 541 having a cap portion 544 corresponding to the seal cap.

FIG. 19 is a schematic cross-sectional view of a mold 93 used for manufacturing the sleeve housing 52 b.

As shown in FIG. 19, the mold 93 includes a dynamic pressure generating groove forming portion 931, a communication groove forming portion 932, and a filling opening 933 through which material for the sleeve housing 52 b is infused into the mold 93. The dynamic pressure generating groove forming portion 931 has a shape capable of forming the thrust dynamic pressure generating groove arrangement 523 of the sleeve housing 52 b. The communication groove forming portion 932 has a shape capable of forming the communication groove 524 of the sleeve housing 52 b. The filling opening 933 is formed on the opposite side of the mold 93 to the dynamic pressure generating groove forming portion 931 so as to be located on the center axis J1 of the sleeve housing 52 b to be formed.

When the sleeve housing 52 b is formed, the mold 93 shown in FIG. 19 is prepared (step S11 in FIG. 6), and then the mold 93 is placed in the injection molding machine. Thereafter, a work-in-process piece for the sleeve housing 52 b having the thrust dynamic pressure generating groove arrangement 523 and the communication hole 524 is formed in a cavity of the mold 93 by injection molding (step S12). The material for the sleeve housing 52 b contains metal particulates having an average particle diameter of 10 μm or less.

After being is taken out from the mold 93, the work-in-process piece is cut along chain double-dashed line A3 in FIG. 19. Then, binders contained in the work-in-process piece are removed by heating and thereafter the particulates contained in the work-in-process piece are sintered (steps S13 and S14). In this manner, the sleeve 52 b is manufactured.

As described above, the sleeve housing 52 b shown in FIG. 18 includes the thrust dynamic pressure generating groove arrangement 523 and the communication groove 524 for pressure adjustment. The hollow cylindrical portion 541 of the sleeve housing 52 b is formed together with the thrust dynamic pressure generating groove arrangement 523 and the communication groove 524 by metal injection molding. Thus, it is possible to efficiently manufacture that sleeve housing 52 b.

In the motor 1 b, the sleeve 51 b may also be formed together with the communication groove 517 by metal injection molding. In this case, the thrust dynamic pressure generating groove arrangement may be formed in the upper end surface of the sleeve 51 b, not in the upper end surface 522 of the sleeve housing 52 b.

FIG. 20 shows another exemplary mold for forming the work-in-process piece for the sleeve housing 52 b. In a mold 93 a in FIG. 20, a plurality of filling openings 933 are arranged at positions of the mold 93 which face outer edges of the upper end surface 522 of the sleeve housing 52 b to be manufactured. Molds having various structures may be used for injection molding for producing the sleeve housing 52 b.

Only selected embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.

In the first to third preferred embodiments, a plurality of spiral grooves are formed. Alternatively, a plurality of herringbone grooves may be formed as shown with 518 in FIG. 21. Moreover, a plurality of communication holes 516 (or communication grooves) may be provided in the sleeve as shown in FIG. 21, or in the sleeve housing.

The bearings of the motors 1, 1 a and 1 b in the first to third preferred embodiments are merely examples. The bearing structure may be changed in accordance with a design of the motor. The fluid in the bearing is not limited to lubricant oil. For example, the bearing may use gas as fluid.

A bearing member other than the sleeve and the sleeve housing may be formed together with a thrust dynamic pressure generating groove arrangement and/or a communication groove (or communication hole) formed therein by metal injection molding. In this case, that bearing member can be manufactured efficiently.

Depending on a design of the bearing, the bearing member formed by metal injection molding may be subjected to additional working or various processing, e.g., plating. A molded product of metal injection molding usually has an excellent spreading property. Thus, it has excellent workability such as for press working or bending work, and has excellent thermal processing property and surface treatment property.

The motors of the above preferred embodiments may be utilized as driving sources of devices (e.g., disk drives such as a removable disk drive) other than the hard disk drive. 

1. A manufacturing method for a bearing member having a thrust dynamic pressure generating groove arrangement which generates a dynamic pressure in a thrust direction between the bearing member and another member, the manufacturing method comprising the steps of: a) preparing a mold provided therein with a portion corresponding to the thrust dynamic pressure generating groove arrangement of the bearing member; b) forming a work-in-process piece for the bearing member in a cavity of the mold by injection molding using a material containing binders and metal particulates having an average particle diameter of 10 μm or less, the work-in-process piece having the thrust dynamic pressure generating groove arrangement; c) removing the binders from the work-in-process piece by heating; and d) sintering the metal particulates in the work-in-process piece to obtain the bearing member having the thrust dynamic pressure generating groove arrangement in which a depth of each groove is 20 μm or less.
 2. The manufacturing method as set forth in claim 1, wherein in the step b), the material is infused into the mold from an opening provided on a side of the mold opposite to the portion corresponding to the thrust dynamic pressure generating groove arrangement.
 3. The manufacturing method as set forth in claim 2, wherein the bearing member has a hollow cylindrical portion centered on a center axis, and the opening of the mold is arranged to face a location at an axially end surface of the hollow cylindrical portion near the center axis.
 4. The manufacturing method as set forth in claim 1, wherein the bearing member has a hollow cylindrical portion centered on a center axis, and in the step b), the material is infused into the mold from an opening provided in the mold which faces a location at an axial end of the hollow cylindrical portion to be formed, the location being near the center axis.
 5. The manufacturing method as set forth in claim 1, wherein the mold has a portion corresponding to a communication hole or groove which adjusts a pressure of fluid in a bearing.
 6. The manufacturing method as set forth in claim 1, wherein the bearing member is one of a sleeve and a sleeve housing.
 7. An electric motor comprising: a stationary portion; a rotor portion; a bearing having the bearing member as set forth in claim 1 and supporting the rotor portion in a rotatable manner around a center axis relative to the stationary portion; and a driving portion rotating the rotor portion around the center axis relative to the stationary portion.
 8. A disk drive for use with a disk-shaped storage medium in which information is storable, comprising: the motor as set forth in claim 7 rotating the disk-shaped storage medium; a head carrying out at least one of reading information from and writing information on the disk-shaped storage medium; and a head moving portion moving the head relative to the disk-shaped storage medium and the motor.
 9. A manufacturing method for a bearing member having a communication hole or groove for adjusting a pressure of fluid in a bearing, comprising the steps of: a) preparing a mold provided therein with a portion corresponding to the communication hole or groove, b) forming a work-in-process piece for the bearing member in a cavity of the mold by injection molding using a material containing metal particulates and binders, the work-in-process piece having the communication hole or groove; c) removing the binders from the work-in-process piece by heating; and d) sintering the metal particulates in the work-in-process piece.
 10. The manufacturing method as set forth in claim 9, wherein the bearing member includes a thrust dynamic pressure generating groove arrangement which generates a dynamic pressure in a thrust direction between the bearing member and another member, the mold has a first portion corresponding to the thrust dynamic pressure generating groove arrangement and a second portion located on an opposite side to the first portion, and in the step b), the material is infused into the mold from the second portion of the mold.
 11. The manufacturing method as set forth in claim 10, wherein the bearing member has a hollow cylindrical portion centered on a center axis, and the second portion of the mold faces a location at an axial end of the hollow cylindrical portion to be formed, the location being near the center axis.
 12. The manufacturing method as set forth in claim 9, wherein the bearing member has a hollow cylindrical portion centered on a center axis, and in the step b), the material is infused into the mold from a portion of the mold facing a location at an axial end of the hollow cylindrical portion, the locating being near the center axis.
 13. The manufacturing method as set forth in claim 9, wherein the bearing member is one of a sleeve and a sleeve housing.
 14. An electric motor comprising: a stationary portion; a rotor portion; a bearing having the bearing member as set forth in claim 9 and supporting the rotor portion in a rotatable manner around a center axis relative to the stationary portion; and a driving portion rotating the rotor portion around the center axis relative to the stationary portion.
 15. A disk drive for use with a disk-shaped recording medium in which information is storable, comprising: the motor as set forth in claim 14 rotating the disk-shaped storage medium; and a head carrying out at least one of reading information from and writing information on the disk-shaped storage medium; and a head moving portion moving the head relative to the disk-shaped storage medium and the motor. 